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sediments which is dominated by higher boiling saturated hydrocarbons.
This phenomenon is unexplained and could represent selective accumulation
and/or retention of lighter aliphatics or more rapid metabolism and
excretion of, heavier aliphatics. The most likely explanation is that
oysters were being contaminated with hydrocarbons leaching from bottom
sediments into the water column. Lighter aliphatics, because of their
slightly higher aqueous solubility than heavy aliphatics, are desorbed
more readily from sediments and therefore are more available for uptake
by the oysters. Aliphatic hydrocarbon fractions of reference oysters
were more uniform (Table 7). Relative abundances of C^q to C32 aliphatics
were similar.
There were no consistent differences in characteristics cf the aliphatic
hydrocarbon fraction between reference oysters and oysters from
oil-polluted Aber Benoit and Aber Wrac'h (Table 8). With one exception
(April 1979), alkane/isoprenoid ratios were higher in oysters from
reference stations than in those from oil-polluted stations. Pristane/
phytane ratios were quite variable and without pattern. All but two
carbon preference indices were near one indicating a petroleum origin
for the high molecular weight aliphatic fraction.
Composition of the aromatic fraction of oysters, as determined by
gas chromatography /mass spectrometry, revealed a great deal about the
origin of the hydrocarbon contamination of the oysters (Tables 9-11) .
High concentrations of alkyl naphthalenes through alkyl dibenzothiophenes
are characteristic of samples contaminated with crude oil. Amoco Cadiz
oil was particularly rich in alkyl phenanthrenes and alkyl dibenzothiophenes.
These were the most abundant aromatics/heterocyclics in oyster
samples from oil-contaminated Aber Benoit and Aber Wrac'h. Aromatic
hydrocarbon assemblages of crude oil origin are dominated by alkylated
species, whereas aromatic assemblages of pyrogenic origin are dominated
by the unalkylated parent compound (Neff, 1979). Thus we can conclude
that oysters from Aber Benoit and Aber Wrac'h at all five sampling times,
and reference oysters from the December 1978 and April 1979 collections
were heavily contaminated with crude oil, resembling the Amoco Cadiz oil.
The other three reference samples contained some oil, but it did not
resemble Amoco Cadiz oil. In oysters from the two Abers, there was a
general trend for the concentration of aromatics/heterocyclics in the
alkyl naphthalenes to alkyl dibenzothiophenes series to decrease
slowly with time. The February 1980 samples contained higher concentrations
of alkyl phenanthrenes and alkyl dibenzothiophenes than expected.
It is possible that winter storms in December and January resuspended
oil-contaminated sediments causing recontamination of resident oysters.
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